Simulium yahense ‘Bioko’

River blindness, or onchocerciasis, is a tropical disease caused by infection with the parasitic worm Onchocercavolvulus.

In Africa it infects around 18 million people, and it is mostly transmitted from person to person by a group of blood-feeding blackflies of the Simulium damnosumcomplex - named as such because they are a 'damned nuisance'.

These different species are very closely related, and can only be identified by chromosomal analysis, but they show very important differences in their ability to transmit the infection to man.

Some do not bite humans at all, but the Bioko form of Simulium yahense was found to be probably the most effective vector of the parasite in the world.

Species detail

The Bioko form of Simulium yahense was discovered in 1990, and is unique to the island of Bioko off the coast of West Africa. It may be a separate species of Simulium, but as it has now been eradicated, we may never know.

Simulium yahense is found in the rain forests of west Africa, where its larvae live in forest streams. The adult female fly needs to take a blood meal to help her eggs develop, and commonly bites humans. Find out more about this fly’s lifecycle.